This invention relates to a new microorganism strain, the enzyme products thereof and processes using same, by which biomass, particularly cellulosic biomass, can be broken down into its simpler components.
The energy crisis which began in the early 1970's focused attention on the need to reduce dependence on fossil fuels. This attention was focused, in part, on the conversion of cellulosic biomass to its simpler sugars, which could then be converted to alcohol via the fermentation process.
The hydrolysis of cellulose and other biomass components is achieved by the action of a group of enzymes called cellulases. (T. M. Wood and S. I. McCrea, "The Mechanism of Cellulase Action with Particular Reference to the Cl Component," Proceedings of Bioconversion of Cellulosic Substances Into Energy, Chemicals and Microbial Protein, T. K. Ghose, ed., pp. 111-41, Thompson Press (India), Ltd., Fariadabad, Haryana, India (1978)).
The cellulase system of Trichoderma reesei (wild strain QM6a and derivatives thereof) is capable of efficiently degrading crystalline cellulose to glucose. That system consists of three different hydrolytic enzymes, endoglucanases (endo-1,4-.beta.-D glucanase EC 3.2.1.4) which attack cellulose derivatives carboxymethyl cellulose and amorphous cellulose, exoglucanases typified in Trichoderma reesei by cellobiohydrolase (1, 4-.beta.-D glucancellobiohydrolase EC 3.2.1.91) and cellobiase (EC 3.2.1.21). Within the above three enzyme groupings, five to eight electrophoretically distinct endoglucanases have been described (V. Farkas, A. Jalanko and N. Kolarova, "Characterization of Cellulase Complexes From Trichoderma reesei QM9414 and Its Mutants by Means of Analytical Isoelectric Focusing in Polyacrylamide Gels," Biochem. Biophys. Acta. 706: 105-10 (1982)); these include two immunologically distinct cellobiohydralases (CBH I and CBH II) (L. G. Fagerstam and L. G. Pettersson, "The 1,4-.beta.-glucan cellobiohydrolases of Trichoderma reesei QM9414: A New Type of Cellulolytic Synergism," FEBS Letters 119: 97-100 (1980); L. G. Fagerstam and L. G. Pettersson, "The Celluloytic Complex of Trichoderma reesei QM9414: An Immunochemical Approach," FEBS Letters 98: 363-67 (1979)), and three cellobiases (C. S. Gong, M. R. Ladisch and G. T. Tsao, "Cellobiase From Trichoderma viride: Purification, Properties, Kinetics and Mechanism," Biotechnology Bioengineering, XIX: 959-98 (1977)).
Previous patents have dealt with the enzymatic conversion of cellulose to fuel, food, and chemicals. For example, U.S. Pat. No. 3,642,580 describes a rapid and complete method of hydrolysis of cellulose into simple sugars employing an enzyme slurry produced from Trichoderma viride (reclassified as Trichoderma reesei in 1977) QM9123 and a suspension of finely ground cellulose. Similarly, U.S. Pat. No. 4,275,163 discloses MCG77, as a new strain of Trichoderma reesei, useful for producing cellulase. The present inventor, with others, has previously disclosed other microbial strains with enhanced cellulolytic enzyme activity, including RUT-NG14, and a screening process that is useful in identifying and selecting microbial strains with enhanced cellulolytic activity. This process also is useful in selecting strains that exhibit less end-product inhibition than unscreened strains.